Carbon in the ring grooves

ravenaviation · Post by **ravenaviation** » Thu Sep 23, 2004 9:32 pm

I just pulled the jugs off my continental for some needed repairs. The piston grooves were very heavily fouled with carbon deposits. Anyone else have this in their airplane? Anything to do to prevent it?

N2363D
John
LaPorte TX (T41)

170C · Post by **170C** » Sun Sep 26, 2004 4:06 pm

Curious---what kind of fuel & oil do you use, how many hours on the cylinders & how often flown?

ravenaviation · Post by **ravenaviation** » Sun Sep 26, 2004 10:12 pm

I use 100LL and Aeroshell 100W plus. The cylinders had about 450 hours on them. Been flying about 50 hours/year (not enough!).

zero.one.victor · Post by **zero.one.victor** » Mon Sep 27, 2004 5:14 am

John, any chance the fouling could be lead (from the 100 "low lead" fuel) and not carbon? I wouldn't wanna ignite the car gas wars again by suggesting you burn auto fuel (

), but maybe there's a local source for 80/87 avgas? 100LL has 4 times the lead of 80/87,which is what our engines were designed to run on. I run a mix of about 75% regular grade cargas & 25% 100LL, which comes as close as possible to duplicating 80/87.

Eric

Post by **GAHorn** » Mon Sep 27, 2004 3:37 pm

Hi, John!
I SOLOED at LaPorte back when castor oil was the preferred motor oil!

Lead is not known for fouling piston ring/lands, but if it did it would ge grey not black or appearing like carbon.
How many hours over how many years has your engine developed "heavily" fouled lands? And what does "heavily" mean? A lot of black carbon? .005" in the bottom of the lands? Or stuck rings due to it?
Manifold pressure is what expands rings against the cyl walls, and the most common cause of stuck rings is operations like skydiving service where high oil and cylinder temps are developed over hot/high climbs followed by rapid cool-down descents. Flight training can sometimes be similar. The oil gets very hot, cokes inside the piston lands, then low manifold pressure allows the rings to "flutter" which lets the hot oil saturate the lands. An engine shut down, expecially pointed downwind on the ramp lets the oil sit there and coke badly. (Always try to point your airplane into the wind for shutdown/tie-down.)
What's my basis for these comments? Purely opinion from the old engine rebuilders at Precision Airmotive who used to service the skydivers down near Houston in the late 60's/early 70's.....so I guess it's anecdotal.
I personally hold the opinion that engines last "overhauled" (repaired actually) with excess ring/land clearances are the problem. I never reuse old pistons when I rebuilt/repair engines for this reason.

ravenaviation · Post by **ravenaviation** » Mon Sep 27, 2004 7:11 pm

It is definitely carbon in the rings. THere was plenty of the crumbly tan lead oxide in the dome of the cylinder, but it was beautiful black carbon (coke) in the grooves. Don't need to debate mogas or MMO or anything else!

George - you are missed here at LaPorte - your solo was the most exciting thing to happen here in a while (except maybe when a certain personality recently gear uppped his Baron - disconnected the warning because it was annoying! Or maybe it was when the Citation went off the end of the runway or... heck I can't remember)

The carbon had pretty much filled the grooves and had immobilized some of the rings. I noticed that the rings might have been cooked at some time because they bent quite a bit before breaking. The engine had 550 hours since major. I did a fair amount of flight training with my son in it, but our SOP is powered descents to keep the engine from windmilling and keeping some pressure on the rings. Of course, there were those hundreds of touch and gos. Might be a previous owner thing, who knows.

Aircraft is hangared, so hope there is no wind!

rudymantel · Post by **rudymantel** » Wed Sep 29, 2004 6:28 pm

"Of course, there were those hundreds of touch and gos. Might be a previous owner thing, who knows. "

I do lots of touch & gos. I keep power on as much as possible in descents and lean mixture till short final. I've wondered if touch & go's can harm my engine. (I use car gas)

BTW, I landed at La Porte a few years ago- nice airport.

Rudy

N1478D · Post by **N1478D** » Wed Sep 29, 2004 7:09 pm

Couldn't count how many touch & go's have been made in 78D! And hundreds of those have been full power till mid downwind climbing the whole time and then chopping to idle to practice dead sticking it on a spot. It has about 1400 hours since overhaul. None of the cylinders have ever been removed, etc. It is flown nearly daily though, and it's my believe that flying an airplane makes up for most other things except things like cold winter starts without preheat, getting the oil too hot, not changing the oil often enough timewise and hourwise, and leaky air intake. All of those things will hurt. The old saying "The best thing you can do is fly her. The worst thing you can do is fly her". Going to be putting on those hours, bet you probably won't make TBO if she's not flown anyway. Don't want to sound like it is daily abuse, but when I want to practice short landings, spot landings, etc. I use the airplane to do it and I will be very surprised if at 1800 hours the mental exercise of overhaul now, or a couple hundred more hours at 2000 or 2200 isn't going on. Compressions still in the 70's, auto gas, daily commute of 12 minutes each way and the belly will get oily over time.

In other words fly, fly, fly, fly, fly, and fly some more. Your plane will love you for it. Some of the owners at the airport have been heard to say "900/1000 hours on those Contential cylinders, I am going to take em off and have em overhauled." Well, those trainers out there on the flight line might have closer to 3000 hours on them before they have their cylinders removed and talk about abuse - but, they are flown often.

N170BP · Post by **N170BP** » Wed Sep 29, 2004 7:31 pm

I hear that.... I fly mine approx. 200 hours per year.
Last annual showed 2 cylinders @ 80/80, the other four
were 78/80. Around 550 SCMOH so far (no stuck valves
or any other problems). I burn 100LL pretty much
exclusively, but the mixture stays lean until I roll
onto the runway for takeoff, and as soon as I set it up
for a cruise climb, it goes back to lean. Upon landing,
the mixture doesn't go rich until short-short final.

I also pretty much fly power @ idle approaches, but am
careful about doing successive reductions in power
(especially while doing pattern work).

Bottom line, the darned thing is running all the time so it
never gets a chance to rust up!

rudymantel · Post by **rudymantel** » Thu Sep 30, 2004 1:10 am

Thanks guys, that makes me feel better about my touch & gos. When I was in the air taxi business in Jamaica (for 22 years) my planes averaged 100 hours per month and always made TBO or more. Average flight times were 30 minutes. But very few touch & gos.
Rudy

Joe Moilanen · Post by **Joe Moilanen** » Thu Sep 30, 2004 7:12 am

Joe and Bela just hit the nail square on top of the head.

Joe Moilanen

170C · Post by **170C** » Fri Oct 01, 2004 11:37 pm

While we are on the subject, I just had a call from my AI (plane getting annual) saying I have 5 cylinders with upper 70's over 80 & one (#2) at 30 over 80!!!!!!! He tried several methods to get the compression up to no avail. He is pulling the cyl to take to Sentry Cylinder here in Fort Worth. Thinks it is a valve (exhaust) problem. I will update as I find out more next week. However, I am just wondering if operational methods could contribute to this problem? I lean pretty much--can you damage exhaust or intake valves by over leaning? I use 100 LL, fly it about 100 hrs annually & run it @ 2500/2600 rpms on trips. Suggestions?

The International Cessna 170 Association

Carbon in the ring grooves

Carbon in the ring grooves

Carbon in Ring Grooves

Cylinders !